Railroad tank cars formed of low-carbon, high toughness, steel plates

Abstract

A railroad tank car formed from steel alloy plates having improved toughness and puncture resistance. The steel alloy plates include a steel alloy including in wt. %: C: 0.1-0.15; Mn: 1.0-1.65; Si: 0.15-0.40; Al: 0.015-0.06; Mo: 0.1-0.3; Ni: 0.1-0.25; Nb: 0.015-0.045; Ti: up to 0.02; Cr: up to 0.22; V: up to 0.08; Cu: up to 0.35; P: max 0.025; S: max 0.015; and N: 0.004-0.01. The alloy plates may have been normalized for 30 minutes at 900° C. The alloy plates may have a tensile strength of at least 560 MPa; a yield strength of at least 345 MPa; a total elongation of at least 22%; a CVN impact toughness of at least 135.5J at −34.4° C.; a CVN impact toughness of at least 122J at −45.5° C. The alloy plates may have a ferrite-bainite microstructure, with 10% or less pearlite. The alloy plates of the inventive railroad tank car may have an absence of any banded ferrite-pearlite/martensite structure.

What is claimed is: 
     
       1. A railroad tank car formed of steel alloy plate, the alloy plate comprising a steel alloy including in wt. %:
 C: 0.1-0.15; Mn: 1.3-1.5; Si: 0.15-0.40; Al: 0.015-0.06; Mo: 0.1-0.3; Ni: 0.1-0.25; Nb: 0.032; Ti: up to 0.02; Cr: up to 0.22; V: up to 0.08; Cu: up to 0.35; P: max 0.025; S: max 0.015; and N: 0.004-0.01, a balance being Fe; 
 the alloy plate having been normalized for at least 30 minutes at 900 degrees C.; 
 the alloy plate having a tensile strength of at least 580 MPa; 
 the alloy plate having a yield strength of at least 460 MPa; 
 the alloy plate having a total elongation of at least 33%; 
 the alloy plate having a CVN impact toughness of at least 156 J at −34.4 degrees C.; 
 the alloy plate having a CVN impact toughness of at least 128.8 J at −45.5 degrees C.; and 
 the alloy plate having a ferrite-bainite microstructure with 10% or less pearlite. 
 
     
     
       2. The railroad tank car as recited in  claim 1  wherein said ferrite-bainite microstructure has 5% or less pearlite. 
     
     
       3. The railroad tank car as recited in  claim 1  wherein said ferrite-bainite microstructure has 1% or less pearlite. 
     
     
       4. The railroad tank car as recited in  claim 1  wherein the alloy plate has been subjected to a post weld heat treatment of 30 to 60 mins at 600 to 650 degrees C. 
     
     
       5. The railroad tank car as recited in  claim 1  wherein the alloy plate is 22 mm thick, and the ferrite-bainite microstructure consists of ferrite, bainite and optionally 10% or less pearlite. 
     
     
       6. The railroad tank car as recited in  claim 5  wherein the alloy plate is normalized for 30 to 60 minutes at 900 degrees C. 
     
     
       7. The railroad tank car as recited in  claim 5  wherein the alloy plate is normalized for 30 minutes at 900 degrees C. 
     
     
       8. The railroad tank car as recited in  claim 7  wherein the alloy plate has been subjected to a post weld heat treatment of 30 to 60 mins at 600 to 650 degrees C. 
     
     
       9. A railroad tank car formed of a normalized and post weld heat treated (PWHT) steel alloy plate, the normalized and PWHT alloy plate comprising a steel alloy including in wt. %:
 C: 0.1-0.15; Mn: 1.0-1.65; Si: 0.15-0.40; Al: 0.015-0.06; Mo: 0.1-0.3; Ni: 0.1-0.25; Nb: 0.032; Ti: up to 0.02; Cr: up to 0.22; V: up to 0.08; Cu: up to 0.35; P: max 0.025; S: max 0.015; and N: 0.004-0.01, a balance being Fe; 
 the normalized and PWHT alloy plate having a tensile strength of at least 580 MPa; 
 the normalized and PWHT alloy plate having a yield strength of at least 460 MPa; 
 the normalized and PWHT alloy plate having a total elongation of at least 33%; 
 the normalized and PWHT alloy plate having a CVN impact toughness of at least 156 J at −34.4 degrees C.; 
 the normalized and PWHT alloy plate having a CVN impact toughness of at least 128.8 J at −45.5 degrees C.; and 
 the normalized and PWHT alloy plate having a ferrite-bainite microstructure with 10% or less pearlite. 
 
     
     
       10. The railroad tank car as recited in  claim 9  wherein the normalized and PWHT alloy plate is an alloy plate that has been normalized for 30 to 60 minutes at 900 degrees C. and post weld heat treated of 30 to 60 mins at 600 to 650 degrees C. 
     
     
       11. The railroad tank car as recited in  claim 9  wherein the normalized and PWHT alloy plate is 22 mm thick, and the ferrite-bainite microstructure consists of ferrite, bainite and optionally 10% or less pearlite.